This is the continuation of a research program that has been analyzing the abnormal stereotyped behaviors common in children and adults with mental retardation, autism, and visual impairment. Among these behaviors are body-rocking, hand-gazing repetitive focusing on objects and ideas, and maintenance of sameness and of routines. One overall aim of the project is to understand these maladaptive behaviors with a view to eliminating them. A second aim is the understanding of the relationship between these abnormal behaviors and similar behavior patterns that sometimes occur in apparently normal people. The proposed program has two sections that are related to one another. The first is a series of studies of the development of stereotyped behaviors in developmentally disabled individuals. The second section is a detailed experimental study of body-rocking in people with severe mental retardation. The studies of body-rocking include three subsections that are concerned with (1) the characterization of the movements; (2) analysis of the feedback maintaining body-rocking; and (3) analysis of the environmental factors that can influence the frequency of expression of the body-rocking motor program.